Spark ignition apparatus for internal combustion engines

1,077,061. Ignition systems. JOSEPH LUCAS (INDUSTRIES) Ltd. Nov.26, 1963 [Dec. 5, 1962; May 8, 1963; June 27, 1963], Nos. 45985/62; 18140/63 and 25576/63. Heading F1B. Spark ignition apparatus for an internal combustion engine comprises a spark generating circuit for supplying spark-generating pulses to the plugs of the engine in turn a trigger circuit coupled to the spark generating circuit and serving to permit the spark generating circuit to produce a single spark producing pulse each time the trigger circuit is biased by an input, a fixed frequency oscillator providing the biasing input to the trigger circuit and magnetic means driven by the engine for preventing the oscillator from providing the biasing input except when a spark is required. Referring to Figs. 1 to 3, when one of the slots 52 appears between the windings 25, 28 the circuit including the transformer 24 the resistor 29, capacitor 31 and transistor 26 oscillates in known manner to produce an A. C. voltage across the resistor 27. The first effect of this voltage will be to render the transistor 35 conductive. When the transistor 35 conducts current flowing through the resistor 38 can flow through the diode 37 and the collector and emitter of the transistor 35 so that the transistor 42 is cut off. Cutting off the transistor 42 causes a high voltage to be developed in the secondary winding 46 of the ignition transformer and a spark is applied to one of the plugs 48. The transformer 32 causes the current in the transistor 35 to build up by regenerative action until saturation is reached at which point the transistor 35 is switched off and the transistor 42 is switched on again. If the transistor 26 and its associated components are still oscillating a further spark will be produced. Thus at speeds below a predetermined value more than one spark will be applied to each plug. Timing may be controlled by a centrifugal advance mechanism and by a known mechanism which is responsive to the pressure in the air inlet of the engine. If desired the air gap may be of such a size that oscillations are prevented from occurring. In this case, as shown in Fig. 6, the core 49 may be U-shaped and the disc 51 is replaced by a spindle including four magnetic arms 72 which permit oscillations when they pass over the limbs on which the windings 25, 28 are wound. In another modification the windings 25, 28 are wound on the same limb of the core so that they oscillate at all times. However the fixed frequency osci